The present invention is directed to the recovery of metal values from manganese deep sea nodules by smelting the nodules under reducing conditions.
A metal recovery process for manganese nodules which requires smelting has generally been downrated. The requirements of having to melt a large amount of material of which only four percent is a desired product is naturally unattractive. The difficult metals separation scheme required for the smelted alloy product is another minus factor.
Indeed, in recent years, much emphasis has been placed on perfecting hydrometallurgical processes for treating nodules to render the copper, nickel, cobalt and molybdenum values leachable. Nevertheless, the high extractions and fast reduction kinetics characteristic of most smelting processes dictate that such a route has certain advantages. In the case of nodules, other advantages of smelting over hydrometallurgical processing include:
1. less steps in ore preparation PA1 2. Elimination of leaching step PA1 3. No requirement for a tailings pond PA1 4. A non-polluting waste product.
A reduction smelting process for deep-sea manganese nodules in which a solid reductant such as coke is utilized as the reducing agent is known. Details of that process are disclosed in Canadian Pat. No. 871,006 entitled "Smelting of Manganiferous Ore Material."
Furthermore, recent research on the reduction roasting of nodules with various carbonaceous reducing agents revealed that, as opposed to coal or gas, a liquid reducing agent such as a petroleum product produces calcines from which a significantly greater amount of the copper, nickel, and cobalt may be extracted by an ammoniacal leach. For details of such reduction roasting, see U.S. Pat. No. 3,753,686.
In the prior art solid reductant smelting process, an amount of a solid reducing material, typically between 2 per cent to 5 per cent, based on the dry weight of the ore material, is necessary to provide for selective reduction of the desired metals. Sufficient fluxing agent, e.g., limestone or silica, is added before or during the smelting operation to provide a fluid slag. Smelting times range from about 1 to about 4 hours. In that process, the reduction of cobalt and copper is enhanced by the addition of sulfur-bearing minerals, such as iron pyrites, in amounts ranging from about 1 to about 15 percent by weight; but, the addition of sulfur bearing materials also reduces a greater proportion of iron and manganese which is undesirable.
As a result of smelting with a solid reducing agent, a metal reduction product is formed which contains most of the desired metals, i.e. copper, nickel, cobalt and molybdenum, and some iron but very little manganese. The principle slag constituents are manganese oxides, iron oxides, and silica.